Uneven number of Panels

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techmuc asked Jul 15, '22

Uneven number of Panels

Hi,

Thanks to @Seb71 help I clarified that I need a new mppt charger for my Balcony setup.

For optical reasons ++. I got them very cheap I have exactly 7 panels with VoC of 22V and Vmpp of 18V (150W). Additionally the panels will be vertical (again optical reason), so will probably only give around 60% of Efficiency. One panel will be in shadow 50% of the time.

I actually wanted to have a parallel setup of 4 panels (including the one in shadow) and 3 panels (the ones only in the sun) in series. After some reading this seems to be idiotic / not working.

What kind of split would you prefer? I am honestly a little bit lost..

3/3 and ignore the 7th one (only optical) would barely reach the battery voltage of 54V (VPPmax 18V*3 = 54..)
7 in series would be very expensive (mppt 250 required..)
3 with mppt 100/20 and 4 with mppt 150/30 gives the same problem as (1)

Thanks for any hint,

Timo

PS: Initial plan was to connect all to a growatt mic 600 (which Has very high max. voltage). I now wanted to evaluate if I can include the Balcony in my normal setup.

charger

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wkirby answered · Jul 15, 2022 at 07:59 PM

This is very tricky. 3 panels is not really going to work very well for you, maybe OK in good sun, but it's likely that the MPP Voltage of the array will be lower than Vbat+1 and then you would not be getting full power from those three.
The 4 in series would be good.
So 4 in series into the 150V controller that you are thinking about buying. 3 in series into the 100/20 and put up will lower power yield a lot of the time.
7 in series would be great as long as your panels have bypass diodes built in. However, yes, a 250V controller would be needed and your existing controller becomes redundant.

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techmuc commented · Jul 15, 2022 at 08:10 PM

The panels have a bypass diode inside - so that's no problem.

Question: 6 in a row with 150V are impossible right? With 0 degrees the 6 in a row will work in 150V. I live in bavaria, so temperatur of at least -20 degree is possible, which forces a 250V controller. Is it correct that higher voltages (VoC, not Vmpp) will crash/destroy the victron charger right?

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Answer 1 · 2022-07-15T20:54:47Z

seb71 answered · Jul 15, 2022 at 08:54 PM

Additionally the panels will be vertical (again optical reason), so will probably only give around 60% of Efficiency. One panel will be in shadow 50% of the time.

You haven't specified the azimuth, but even if facing South, frankly, don't bother with this PV array.

60% is highly optimistic for those conditions.

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techmuc commented · Jul 15, 2022 at 09:00 PM

They are facing south, yes. I will probably add sth like 10 to 20 degrees (I will see how that looks like) - as per what I found, while 90 degree gives only 69% max, 80 degree already gives 85%..

PS: I guess you are right though: I will simply use the growatt mic, and use it as a normal balcony setup. This will be <800€ in total.. Not good not super bad. (at least better than investing 800€ in the mppt alone)

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seb71 techmuc commented · Jul 15, 2022 at 10:20 PM

If you can/are allowed to install the panels at 45 degrees or so, then it would be much better.

Also, can't you do anything about that shadow? If it's from a tree, maybe you can prune it. Or leave a gap there (no panel installed in the area with the shadow).

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